Electrochemically Driven Gas Phase Ethylene and CO Oxidation on Pt/Yttria-Stabilized Zirconia Catalysts

Solid electrolytes such as yttria stabilized zirconia (YSZ) and doped-ceria (Sm-CeO 2 or Gd-CeO 2 ) are widely used in the fuel cells, sensors and in heterogeneous catalysis, particularly in electrochemical promotion of catalysis (EPOC) [1, 2]. The bulk ionic O 2- conductivity of YSZ is caused by the presence of oxygen vacancies and becomes significant above 600 °C. Several recent studies showed that YSZ can finely disperse and stabilize nanoparticles and strongly enhance the catalytic activity of nanostructured catalysts through the action of the thermally induced O 2- promoters [2], which makes it very promising support material in heterogeneous catalysis [1-4]. Recently [3,4], we reported the oxidation of CO and ethylene over Pt nanoparticles (NPs) with the average size of 2.5 ± 0.5 nm deposited on ionic and mixed ionic-electronic conductors (MIEC) supports: YSZ, ceria (CeO 2 ) and samarium doped-ceria (SDC) in the absence of oxygen in the gas feed. The full conversion of 909 ppm of CO and C 2 H 4 by reaction with lattice O 2- from the conductive ceramic supports was achieved in the temperature range of 120–240 °C depending on the support. The conversion was observed already at temperature as low as 70 °C indicating that surface O 2- is an active reactant, because bulk ionic conductivity of YSZ, ceria and doped-ceria is insignificant below 350 °C. The proposed redox mechanism of CO and C 2 H 4 oxidation by O 2- involves formation of local nano-galvanic cells at the three-phase boundary (tpb), that is, Pt NPs/conducting ceramic support/gas phase, where anodic and cathodic processes occur simultaneously but separated in space. The anodic reaction is CO or C 2 H 4 electro-oxidation by oxygen ions from YSZ and/or carbon oxidation that can cover Pt surface during CO and C 2 H 4 oxidation. Whereas, the cathodic reaction is the partial surface reduction of zirconia or ceria at the three-phase boundary (tpb). In the present work, we present the Pt particle size effect on the oxidation of CO and ethylene in the absence of O 2 in the gas feed [4]. NPs of Pt with four average particle sizes, 1.9, 3.0, 4.4 and 6.7nm, were synthesized using the polyol method and ethylene glycol as a reducing and stabilizing agent. Scanning transmission electron microscopy (STEM) coupled with energy-dispersed X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used to evaluate Pt/YSZ properties. Furthermore, CO and ethylene oxidation in the presence of 3.5 kPa